The present invention relates to a magnetic tape device such as a DAT (digital audio tape recorder), and more particularly to a magnetic tape device having catchers mounted to a drum base so as to ensure a perpendicularity of guide posts.
FIG. 5 is a plan view of an essential part of a DAT as the magnetic tape device in the prior art, and FIG. 6 is an elevational view of FIG. 5. Referring to FIGS. 5 and 6, the DAT includes a deck base 1 formed from a sheet metal, a pair of tape guide holes 2 formed through the deck base 1, a drum base 3 formed from a zinc die cast and fixed to the deck base 1 by means of first screws 4, a pair of catchers 5 formed from a zinc die cast and integrally formed with the drum base 3 at the front ends on the opposite sides of the drum base 3, a motor 6 fixed to the drum base 3, a fixed drum 7 fixed to the drum base 3 by means of second screws 8, a rotating drum 9 adapted to be rotated through a rotating shaft 10 of the motor 6, and a magnetic head 11 mounted on the rotating drum 9.
FIG. 7 is an elevational view of tape guide means 12 adapted to be moved along each tape guide hole 2. The tape guide means 12 is constructed of a support member 13 for supporting the tape guide means 12, a guide post 14 and a positioning post 15 extending from a lower end of the guide post 14. Each catcher 5 includes an upper stopper 16 and a lower stopper 17.
In operation, a magnetic tape (not shown) in a cassette (not shown) is pulled out by the tape guide means 12 moving along the tape guide holes 2, and is brought into contact with the rotating drum 9 and the fixed drum 7, thus reading signals on the surface of the magnetic tape. At this time, the magnetic tape is inclined at a predetermined angle (which will be hereinafter referred to as a tape inclined angle) with respect to a rotating surface of the magnetic head 11. Further, each positioning post 15 is brought into contact with the upper stopper 16 and the lower stopper 17 of each catcher 5 to thereby ensure the perpendicularity of each guide post 14.
In the above-mentioned prior art DAT, the drum base 3 and the catchers 5 are formed from a zinc die cast, while the deck base 1 is formed from a sheet metal which is low in cost. Thus, the deck base 1 and the drum base 3 formed of different materials are fixed together through the first screws 4. That is, coefficients of thermal expansion of the deck base 1 and the drum base 3 are different from each other. As a result, a change in peripheral temperature causes different amounts of expansion or contraction of the deck base 1 and the drum base 3, thereby generating distortion in shape of at least one of the deck base 1 and the drum base 3. Accordingly, there occurs an error in positional relationship between the deck base 1 and the drum base 3, with the result that the tape inclined angle cannot be maintained constant, and the perpendicularity of the guide posts 14 cannot be ensured. As a result, the magnetic head 11 cannot properly read the signals. Further, there is another problem that the catchers 5 formed from a zinc die cast must be machined to ensure an accuracy after forming.